The present invention relates to a process for producing a molded article comprising a mixture of an olefin resin and hydrolyzed ethylene-vinyl acetate copolymer, wherein the long run processability during the melt-molding (hereinafter referred to as "long run processability") and qualities of molded articles can be remarkably improved.
Various molded articles can be obtained by melt-molding a mixture of an olefin resin such as polyethylene or polypropylene, and hydrolyzed ethylene-vinyl acetate copolymer (hereinafter referred to as "EVOH"). Objects of the above-mentioned technique are as follows:
(1) To obtain physical properties, which cannot be expected from employing only one of the said resin, as described in, for instance, Japanese Examined Patent Publication (Tokkyo Kokoku) No. 1032/1967 and No. 44579/1974, Japanese Unexamined Patent Publication (Tokkyo Kokai) No. 7038/1973, No. 65544/1975 and No. 122950/1983, and the like.
(2) To reuse useless portions of molded articles, that is, scraps or cut edges of the molded articles which are obtained during the production of laminated moldings of the olefin resin and the EVOH, or inferior goods.
From the view point of the industrial practice, the object of item (2) is more important.
However, when the molded articles such as laminated films or sheets are produced by means of the melt-molding with the above-mentioned mixture of resins, a gelled resin, a colored or carbonized resin during thermal degradation happens to adhere to an inner wall of an extruder during the molding. And after all, there is occurred a problem that the melt-molding cannot be continuously carried out for a long period of time, that is to say, so-called long run processability becomes poor. Also, a gelled material is often incorporated into the molded article during the melt-molding, which results in the quality deterioration such as occurrence of fish eyes during the film-molding.
To solve the above-mentioned problems is particulary important when reusing waste products of laminated moldings (scraps or cut edges of laminated moldings, inferior goods and so on) from the olefin resin and the EVOH.
In fact, recently, it is unusual that each of the olefin resin and the EVOH is employed singly for producing films, sheets, containers or bottles for wrapping or packaging. That is to say, it is usual that they are employed as the laminated molding, the molding constitutes of two, three or more layers and sometimes there are adhesive layers between the layers, if necessary. Because in the market the wrapping or packaging materials are required to have more super properties. However, when the laminated moldings are produced, a lot of scraps or cut edges of the laminated moldings or inferior goods and so on are generated. Accordingly, the recycling of the waste products of laminated moldings is strongly required in the industry.
Of course, the lack of long run processability becomes problem very rarely even when the EVOH or the olefin resin is used singly, but it becomes more serious in case of using a mixture of the EVOH and the olefin resin. In the melt-molding, screen meshes are often choked with the gelled materials, or melted resins adhere to a screw in an extruder frequently. As a result, there is required remarkably troublesome operation, that is, disassembly of extruder and the cleaning of screen meshes or the screw at every time when screen meshes are choked or the melted resins adhere to a screw.
Recently, for solving the above matter, Japan Tokkyo Kokai No. 199040/1985 has suggested a process in which a salt or an oxide including at least one element selected from the group consisting of elements of groups (I), (II) and (III) in the periodic table is added to the mixture of the olefin resin and the EVOH. According to the description of the Tokkyo Kokai, it is recommened that the above-mentioned salt or oxide is added to the EVOH, the mixture is thoroughly kneaded, the olefin resin is added to the kneaded mixture, and then the mixture is melt-molded. However, the satisfactory effects cannot be obtained from the above-mentioned process, for instance, as to the improvement of the long run processability, the melt-molding can be continuously carried out for about 48 hours at most. It goes without saying that, the longer the melt-molding can be carried out continuously, the more advantageously it can be done industrially.
An object of the present invention is to provide a process for producing a molded article, wherein the long run processability and qualities of molded articles can be remarkably improved
This and other objects of the present invention will become apparant from the description thereof